All you have to do is search those roleplays until you find one that interest you, and then, if you see that the roleplay is accepting, then you would have to follow and paste a guide line - a Sign Up Sheet. (which I reccomend you do it if they have posted an OOC - Out of Character thread at the Roleplay Lounge).
Try to follow the requirements as best you can, and then, if they accept you, you can start roleplaying! Usually they'll post a IC thread - which is the actual thread that you would roleplay in, at the Roleplay Corner.
When you start roleplaying, just remember what they ask you to do as you post (like specific events or tasks they could ask you to do) and you should be good to go from there. :3
Howdy Miss Doronjo, you're my mentor? yes? thanks for taking me in and....uhh....can you teach me a few things about the rules of pokemon roleplaying here? are there any threads (or boards) for that? can you direct me there? uh-oh....I'm asking too many questions again....s-sorry....